1. Field of the Invention
The present invention relates to a billiard game system that causes a player to shoot a simulative ball and an input device and computer program suitable to such a game system.
2. Description of the Related Art
As an input device of a billiard game system that reproduces a feeling of shooting a cue ball, in Japanese Patent Application Laid-Open No. 2001-178966 (hereinafter, referred to as reference 1), there is disclosed an input device comprising: a simulative ball supported by a guiding mechanism; a shooting signal output device for outputting a signal that corresponds to a shooting force when the simulative ball is shot by a cue or its substitute or a displacement speed of the simulative ball; and a shooting point signal output device for outputting a shooting point signal that corresponds to the shot position of the simulative ball.
In Japanese Patent Application Laid-Open No. 2000-93655 (hereinafter, referred to as reference 2), there is disclosed an input device in which: a tip end of a rod simulating a cue is housed in a predetermined case in a state in which the tip end can be moved in its axial direction; a magnet is mounted on the tip end of the rod, and a coil is disposed at the periphery of its tip end; and when the rod moves in the axial direction, a cue ball shooting speed is specified based on a dielectric current generated at the coil.
In U.S. Pat. No. 6,220,963 (hereinafter, referred to as reference 3), there is disclosed an input device comprising: a housing such as a mouse utilized as a computer's pointing device; and a receiving portion mounted on the housing, the receiving portion supporting the tip end of the cue, wherein a cue operation is detected by means of an optical reader and an optical reading roller mounted on the housing or the receiving portion.
In an actual billiard game, there exist a variety of shots for shooting the cue ball in a specific direction off its core such as follow shot, draw shot, or jump shot, and a variety of operations are provided to the cue ball by these shots. However, as in the input device of reference 1, in the case where a simulative ball is supported by a shaft, movement of the simulative ball is restricted more significantly than an actual cue ball according to its support structure. Thus, depending on a position at which the simulative ball is shot (a shooting point) or a shot angle, a feeling when the actual cue ball is shot cannot be reproduced sufficiently.
In the input device described in reference 1, the simulative ball is structured so that the simulative ball can be divided into two sections, i.e., a side at which the player shoots and its opposite side. A hemispherical portion at the side at which the player shoots is connected to a volume detector of the inside of the simulative ball. Then, a shooting point of the simulative ball or an angle at which the ball is shot is detected based on an output of such a volume detector. In the case where the simulative ball itself is thus divided into sections, as the simulative ball itself is displaced, it is difficult to reproduce the feeling when the actual cue ball has been shot and the construction of the simulative ball becomes complicated as well. In addition, in reference 1, there is disclosed an example wherein a pressure sensing film or a pressure sensing rubber is provided on a surface of the simulative ball, thereby detecting a shooting point and an angle at which the ball has been shot. However, in this case as well, the feeling when the simulative ball has been shot changes depending on a material for such a pressure sensing film or pressure sensing rubber, thus it is difficult to reproduce the feeling when the cue ball has been shot in the same way as that described previously.
In the input device of reference 2, no simulative ball essentially exists, and the feeling when the cue ball is actually shot cannot be reproduced. Moreover, the input device of reference 2 is arranged to hold the tip end of the rod simulating the cue in a case. Thus, it is required to rotatably provide the case itself in the horizontal direction or vertical direction around a predetermined fulcrum in order to change the rod operation direction. As a result, the rod operation is restricted to a rotational motion around the fulcrum of the case, and thus the player cannot carry out an operation such that the player shoots a cue in an arbitrary direction relevant to the cue ball. Therefore, rod operation is different from actual cue operation, and in this respect as well, the reality is degraded.
The input device of reference 3 as well is not arranged to shoot the simulative ball, and the feeling when the cue call is actually shot cannot be reproduced. In addition, in the input device of reference 3, a variety of detecting devices are built in the housing or the receiving portion, thus making it necessary to operate the cue while the tip end of the cue is guided by its receiving portion. Thus, a shot using a rest (referred to as a bridge) formed by the player's fingers cannot be carried out, and actual cue operation cannot be sufficiently reproduced. Further, in the device of reference 3, when the receiving portion is pushed down by the cue, a signal indicating that the cue ball has been shot is generated. Such an operation is unnatural, and the reality of shots is further degraded.